In the exploration of oil and gas, hydrocarbon seeking entities often employ Measurement While Drilling/Logging While Drilling (MWD/LWD) services to measure and collect drilling and/or formation information in real time while drilling (as the name suggests). In their quest, these entities seek out drilling service companies that specialize in such services as directional drilling, formation evaluation, and other oil-well drilling/planning operations. These services companies will then bring various electronic “down-hole tools” to a well site and insert them into the drill string near the drilling bit to sense drilling or rock properties, acquire, process, transmit and present the real-time information as the well is being drilled.
In addition to providing MWD/LWD measurements, the downhole tools facilitate directional drilling. Directional drilling employs a surveying instrument that estimates the orientation and optionally the position of the bit. The surveying instrument is coupled with a steering mechanism that enables the driller to navigate the borehole relative to subsurface regions of interest.
The assembled downhole tools are often collectively referred to as the Bottom-Hole-Assembly (BHA) that includes a telemetry module for communicating with the surface. The BHA transmits a representation of a least a subset of the measured/logged data to the surface, where it is processed and presented to a user as a log report. Often, this data is of a digital format and may subject to a variety of compression techniques. There are a variety of transmission methods including but not limited to mud pulse telemetry, electro-magnetic telemetry, acoustic telemetry and wired-pipe telemetry. Of these, mud pulse telemetry has proven most popular due to its reliability.
Mud pulse telemetry (MPT) exploits the drilling rig's plumbing system. In most drilling operations, a circulation pump circulates fluid through a drill string and out the drill bit into a borehole, where it returns along the annulus to the surface. This fluid (often called “mud” in the oilfield industry) may include water and/or oil and one of a plurality of additional additives that may be inert or chemically reactive with other molecular compositions present within a borehole during drilling operations. There are a multitude of motivations for pumping mud with one example being simply to remove earth materials from the borehole.
A service company may install at least one transducer/sensor within the rig's plumbing system. The surface rig's plumbing system mechanically connects the so-called mud-pump(s) with the drill-string which in turns couples with a drill-bit within the borehole. The purpose of these surface transducers/sensors is to enable the acquisition of encoded waveforms transmitted from a “pulser” down in the BHA. Thus, MPT systems serve to communicate real-time information through a mud column within a drill string via a series of modulated pressure waves that are supposed to be detected by the surface transducers/sensors.
Unfortunately, signal energy dispersion in the fluid and noise sources (e.g., from the circulation pump) often hinder the operation of the MPT system. Various precautions may be employed such as usage of pump dampeners (a.k.a. “de-surgers”), careful positioning of the transducer, and directional detection. Such precautions are usually helpful, yet there remain opportunities to further enhance telemetry system performance.
It should be understood, however, that the specific embodiments given in the drawings and detailed description do not limit the disclosure. On the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and modifications that are encompassed in the scope of the appended claims.